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c++cextern

How to detect if C code (which needs 'extern C') is compiled in C++

I have a C header as part of a C++ library.

This C header would only make sense compiled by a C compiler, or by a C++ compiler within an extern "C" { ... } block, otherwise unresolved link errors would happen.

I thought to add a block such as:

#ifdef __cplusplus
#error "Compiling C bindings with C++ (forgot 'extern \"C\"'?)"
#endif

in the C header, but unfortunately the __cplusplus macro is defined also within an extern "C" { ... } block.

Is there another way to detect this condition correctly?

Solution

  • The common practice is not to demand client code wraps your header in extern "C", but to do so conditionally yourself. For instance:

    #ifdef __cplusplus
extern "C" {
#endif

  // Header content

#ifdef __cplusplus
}
#endif

    That way client code is automatically correct without doing anything beyond including the header.